With an open mind and a refined palate Mariano Casotti brought the spoonful of genetically modified Californian tomato puree to his mouth and tasted the future. "Not much difference," he said of the puree, on sale for the first time in Sainsbury and Safeway stores yesterday. He smacked his lips and went back to his traditionally grown Italian puree for further comparison.

What Mr Casotti does not know about pasta and sauces is probably not worth knowing. For 35 years the assistant executive chef to Spaghetti House has been up and making pasta by the tubful while the rest of the country has scarcely thought of breakfast.

But taste, he says, isn't everything. "The colour is very rich and dark which could deaden the colour of meat in a bolognese sauce. And the texture is slightly rougher … more starchy," he said, absent-mindedly patting both dishes of red goo smooth with the bottom of his spoon.

He conferred in Italian with Riccardo Lavarini to ensure the two connoisseurs spoke with one, satiated, tongue. "Without comparing actual dishes it is a little difficult to say but usually we use puree just for colouring the sauces," said Mr Lavarini, the director of Spaghetti House. "I must say I'm a little uncomfortable with the name. People like to think that they are getting freshly prepared food. This sounds a little too scientific."

It took 21 years of research to produce the 29p can of puree in question. The big breakthrough came in 1986 when they isolated the enzyme which accelerates the rotting process in tomatoes, allowing growers to produce longer-lasting, firmer-textured fruit.

The benefits are that firmer tomatoes will not go squashy when they are handled; more tomatoes are harvested; more arrive at shops intact and once there they do not deteriorate as quickly.

The Sainsbury's version comes with a special leaflet reassuring customers that all ethical considerations have been taken into account. It has even earned the approval of their advisory committee on genetic modification. "We treat the ethical issues relating to genetically modified products on a case by case basis. With tomatoes there did not seem to be a problem," said a Sainsbury's spokesman last night, insisting that demand will determine how long it remains on the shelves.

For the sceptics there is [a] freefone number for further explanation. For those who just want something cheap and tasty to put on their pizza bases most of the information is on the tin. But for Mr Casotti the proof of the puree, genetically modified or not, will always be in the eating.